1. Field of the Invention
The present invention relates to a printing apparatus and printing medium roll-up state discrimination method. Particularly, the present invention relates to a printing apparatus which prints on a rolled printing medium with an inkjet printhead, and a printing medium roll-up state discrimination method.
2. Description of the Related Art
A conventional inkjet printing apparatus has a printhead on which a plurality of ink discharge nozzles (to be referred to as nozzles hereinafter) are arrayed in the printing medium conveyance direction (subscanning direction). A carriage which supports the printhead reciprocates in the moving direction (main scanning direction). At the same time, the conveyance roller repetitively conveys the printing medium in the subscanning direction, thereby printing on the entire printing medium.
Some printing apparatuses of this type can print on roll paper in addition to regular-size sheets such as A4 and A3 sheets. The roll paper is prepared by rolling printing paper elongated in the longitudinal direction (conveyance direction when the paper is set in the printing apparatus).
Methods of handling roll paper printed by a printing apparatus of a type which prints on roll paper are classified into two methods: One is to cut a printed part and discharge it into a basket after one printing job, and the other is to roll up printed roll paper around a dedicated spool and store it. According to the latter method, roll paper must be rolled up stably while controlling its roll-up state, and if an error occurs in the roll-up operation, the error must be detected reliably.
For example, Japanese Patent Laid-open No. 2002-002035 proposes a method of implementing stable roll-up. This method assumes a configuration in which roll paper discharged along with the progress of printing rotates while pressing a roller connected to an encoder scale in the printing apparatus. In this printing apparatus, a photo-interrupter detects the rotation of the encoder scale which rotates together with the discharged roll paper, thereby detecting the paper feed state. In accordance with the detected state, driving of the motor of the roll-up unit is controlled.
As a similar technology, for example, Japanese Patent No. 2,665,499 proposes a conveyance control method aiming at stable feed of a roll film in an exposure apparatus. According to this method, a roll film is slack before and after the exposure point in the exposure apparatus. Different sensors detect slack states before and after the exposure point, and different motors control feed of the roll film before and after the exposure point in accordance with outputs from the sensors, preventing an excessive load on the film.
However, if the roll-up unit cannot accurately roll up roll paper, the technique disclosed in Japanese Patent Laid-open No. 2002-002035 cannot discriminate this state as an error. Roll paper is pulled toward the roll-up side by setting the rotational speed of the motor on the roll-up side faster than that on the printing side. Thus, even if roll paper suffers strong pull, this cannot be detected.
The technique disclosed in Japanese Patent Laid-open No. 2002-002035 is effective under operating conditions free from any actual damage, for example, in a case where roll paper is small in size and its printed surface does not get dirty even upon contact with a roller or the like immediately after printing, just like roll paper set in an automatic teller machine (to be referred to as an ATM hereinafter) at a bank. However, this technique cannot be applied to a case where a printed image may be negatively affected if another member directly contacts the printed surface immediately after printing, like an inkjet printing apparatus.
The technique in Japanese Patent No. 2,665,499 discloses a method of controlling the slack amount of a roll film within a predetermined range. However, this patent does not describe error detection when, for example, a film is caught by the slack generating portion, and error removal processing upon generation of an error. A guide is arranged at the slack generating portion for the purpose of stable detection by the sensor. In an inkjet printing apparatus, however, it is impossible for the above-described reason to move printing paper immediately after printing along the guide.
Hence, demand has arisen for a method other than the conventional arts in order to reliably detect a roll-up error of a printing medium after printing regardless of its size or type and stably keep rolling up the printing medium in an inkjet printing apparatus using roll paper as a printing medium.